1. Field of the Invention
The invention relates to fluoropolymer-containing lidding films for food, non-food and medical packages. More particularly, the invention pertains to a two-piece sealed package, including container and lid portions, which are separable from each other.
2. Description of the Related Art
It is well known in the art to provide containers such as tubs, cups, jars and pails which are useful for packaging, distributing and serving food, non-food and medical items. Typically, such containers are provided with a lid material, which seals its opening and yet is easily peeled off for access to the container contents. The lids are usually made from multilayer sheets which are die cut into a desired shape or heat sealed to a base cup stock then die cut as the final process of the packaging operation.
Many lids are made of one or more layers of polymers in order to achieve certain desired properties, particularly moisture and oxygen barrier properties. For example, a multilayered lidding film may have one polymer layer that serves as a water or solvent barrier and a second polymer layer that serves as an oxygen or air barrier. A typical moisture or solvent barrier polymer is a polyolefin such as polypropylene or polyethylene and a typical oxygen barrier polymer is a polyvinyl alcohol, an ethylene vinyl alcohol copolymer, a polyvinylidene chloride, a nylon, a polyacrylonitrile or a polyester. It is also known to laminate foil layers, such as aluminum foil, to polymer layers to add other desirable properties. Processes for producing these laminates are well known. If two thermoplastics are compatible, they can be combined by coextrusion to form a composite structure or laminated by melting the surfaces of the layers in contact with one another and by applying pressure. If the two thermoplastics are not compatible, they can be made into a laminate by placing an adhesive layer between the incompatible layers.
Many fluoropolymer materials, particularly films formed of poly(chlorotrifluoroethylene) (PCTFE) homopolymers and copolymers, are commonly known for their excellent moisture and vapor barrier properties, and therefore are desirable components of packaging films. Oriented fluoropolymer films have also been shown to exhibit improved moisture barrier properties over non-oriented fluoropolymer films. Methods of making films and film structures from PCTFE polymers and copolymers are known in the art. These are shown, for example, in U.S. Pat. Nos. 6,555,190; 6,432,542; 6,306,503; 5,945,221; 5,874,035; 6,238,607; 6,465,103 and 5,139,878.
U.S. Pat. No. 4,544,721 to Levy discloses stretched or oriented films of PCTFE homopolymers and copolymers. U.S. Pat. No. 4,677,017, which is incorporated herein by reference, discloses coextruded multilayer films which include a fluoropolymer and a thermoplastic film which are joined by the use of an adhesive polymer. U.S. Pat. No. 4,659,625, which is incorporated herein by reference, discloses a fluoropolymer multilayer film structure which utilizes a vinyl acetate polymer adhesive layer. U.S. Pat. No. 5,139,878, which is incorporated herein by reference, discloses a fluoropolymer film structure using an adhesive layer of modified polyolefins.
These films and structures formed therefrom have been used in packaging applications, yet have not heretofore been used in lidding film applications. It is particularly desirable to have a fluoropolymer containing lid for a container which lid has a shape that conforms to the shape of an opening of the container.